There are already known various processes for molding parts made out of a composite material, allowing shaping said material, which consists of fibers embedded in a thermosetting or thermoplastic matrix, by means of a mold and in association with particular pressure and temperature conditions.
The fibers are generally made out of glass, carbon or aramid, while the matrix is of the epoxy, phenol or similar type.
The known processes also differ according to the way the composite material is implemented in the mold. Most of these processes use a mat in the form of a non-woven web of fibers extending parallel to each other, and from which are taken either plies aimed at being superposed eventually while changing the orientation of the fibers, in order to increase the strength of the whole, or more or less long and/or wide pieces that are arranged in the mold, said pieces of pre-impregnated web being arranged loose at random or according to a particular tri-dimensional arrangement in connection with the use of the part to be made.
One should note that the pieces of pre-impregnated web can be formed into a structure made outside the mold, which allows arranging the fibers according to a preferred orientation, and thus obtaining an increased resistance against a known effort. This way of operating is however time-consuming.
EP 0,025,689 discloses a complex manufactured by such a process, and which consists of a sheet made by assembling two sheets made, in turn, by assembling pieces cut out of a web of pre-impregnated fibers.
From FR 2,740,149 is also known a process for molding from a sheet made by assembling pieces of a web of pre-impregnated fibers. The pieces of web are superposed horizontally and at random, in order to form a structure that is then subjected to a pressure in the range of 10 to 80 kg/cm2 and to a temperature in the range of 210 to 350° C.
On the other hand, EP 0,916,477 discloses a process for molding a part made out of a composite material, starting from a composite structure formed by assembling pieces of a web of pre-impregnated fibers, in which said pieces are so arranged as to achieve a tri-dimensional arrangement of the fibers, said structure being then subjected to a temperature in the range of 150° C. and to a pressure in the range of 10 to 100 bars.
One should note that during the putting under high pressure there has thus been observed some flowing of the thermosetting or thermoplastic material, which can be assimilated to a draining of the fibers, so that the part obtained has a low strength.
The above-mentioned processes are for manufacturing particular objects, thus the process of FR 2,740,149 is intended for manufacturing reinforced tips of shoes, while the process of EP 0,916,477 is mainly intended for manufacturing objects such as cranks for the crank-gear of a bicycle. Though these objects have a high strength, it is nevertheless limited, which does not allow manufacturing certain parts that have a somewhat complex shape.
For instance, in the case of hollow parts having joining elements with different axes, it is necessary to use a core around each portion of which ply cushions are arranged, then to place the whole in a mold under pressure. One observes however a very bad connection between the different elements, since it results only from the flowing of the thermosetting or thermoplastic matrix.
Furthermore, in the particular case of an object having one or several through holes, it is possible to proceed in various ways.
A drilling can be carried out after molding, with, besides the difficulty due to the hardness of the material, the inconvenience of severing the fibers, which results into a relative weakness in the vicinity of the hole.
As in the earlier EP 0,916,477, one can also use an insert or core arranged in the mold and, eventually, wind pieces of a web of pre-impregnated fibers around this insert or core, which gives rise to risks of discontinuity in the network of fibers over the complete manufactured object.
Furthermore, the presently known processes require, after removal from the mold, labor-expensive machining and deburring work that can be prejudicial to the strength of the manufactured object.
From EP 0 355 641, JP 02 131929 and EP 0 755 772 are also known processes for manufacturing, through molding, objects made out of a composite material, in which it is foreseen to carry out steps of shaping, eliminating material in excess, pressing and heating, then cooling. One could observe that the objects obtained by means of the processes disclosed in these documents have no homogenous strength, namely because of said processes and because of the devices allowing implementing them.
The present invention is aimed at coping with these various drawbacks by providing a process for molding a part made out of a composite material that namely allows manufacturing parts having a higher strength than the parts obtained by means of the presently known molding processes, irrespective of the complexity of that part.
The process for molding a part made out of a composite material according to the invention is of the type consisting in placing in a mold a pile of plies taken from a web of fibers embedded in a thermosetting or thermoplastic material, and arranged according to preferred directions of said fibers, and in subjecting said mold to particular pressure and temperature conditions, and it is characterized in that it consists in carrying out successive operations of:                shaping said pile of plies in the mold, at low pressure, carried out progressively at low speed;        removing the material in excess protruding out of the edge of the mold;        carrying out the tightness of the mold from outside;        increasing the pressure up to high pressure;        raising the temperature of the mold; and        quickly cooling the mold.        
The process according to the invention allows carrying out a real forging of the composite material, which grants the obtained part very high strength, which allows contemplating the manufacture of parts manufactured so far out of metal, for example aluminum.
The existing processes, namely those disclosed in EP 0 355 641, JP 02 13 1929 and EP 0 755 772, do not allow achieving this result, indeed, removing the material in excess is carried out prior to shaping and prior to putting under pressure, so that the quantity of material used is not optimal, and cutting during pressing generally causes flowing of the thermosetting matrix, which results into a weakening of the part obtained through molding.
In addition, in the processes of the above-mentioned documents, it is not foreseen to carry out the tightness of the mold, so that one observes flowing of the thermosetting or thermoplastic matrix.
According to an additional feature of the process according to the invention, the high pressure is between 50 and 200 bars, while the heating temperature for the mould is between 125 and 135° C.
One should note that using a pressure up to 200 bars is possible only because of carrying out the tightness of the mold from outside, otherwise, a draining of the fibers is observed.
According to another additional feature of the process according to the invention, the operation of removing the material in excess is associated, when the part to be manufactured should include one or several through-holes, to an operation of punching through the mold.
Simultaneously with the removal of the material in excess there is carried out a punching through the mold, and the punch or punches or die-cutters are kept in place during the pressing and heating operations.
When starting punching, the fibers are not immediately cut, so that after cutting, their ends are oriented along an axis different from their main axis, which provides the edge of the hole with a particular strength, which does not allow obtaining, for example, a drilling and removing operation.
One should note that there is also obtained a re-orientation of the ends of the fibers at the periphery of the part when cutting the material in excess.
One should note that punching is carried out after shaping within the mold under low pressure, which is very important. For example, in EP 0 355 641, a punching is indeed carried out in the mold prior to shaping and prior to putting under pressure, or then simultaneously and not successively, which results into a risk of flowing of the thermosetting matrix and also of suppressing some fibers, and hence, of not achieving any forging.
For manufacturing complex parts, such as those evoked above, for example, hollow parts including several joining elements with different axes, the putting under pressure with tightness of the mold allows, since there is no draining, the fibers to flow, so that there is an interweaving of the fibers of a cushion for the manufacture of one of said elements with the fibers of one or several other cushions, so as to achieve a very strong part.